Improved thermal stability of an organic zeolite by fluorination

The thermal stability of an organic zeolite material, namely 2,4,6-tris(4-bromo-3,5-difluorphenoxy)-1,3,5-triazin (Br-3,5-DFPOT), was improved by fluorination of 2,4,6-tris(4-bromophenoxy)-1,3,5-triazin (BrPOT). The open pore structure (van der Waals diameter of 10.5Å) of the modified zeolite was observed up to 110°C in comparison to 70°C for BrPOT. Nitrogen sorption at low temperature showed a type I isotherm and derived pore volumes thereof are in agreement with structural data. It was observed here that Br-3,5-DFPOT crystals preserving the open pore structure could only be obtained below a typical size of about 50μm. The improved thermal stability of the fluorinated system is attributed to an enhancement of the strength of the Br3-syntho

Novel Host-Guest Structures of 2,4,6- Tris (4-Halophenoxy)-1,3,5-Triazines(XPOT): Inclusion of C60 and Pyridine

The crystal structures of two halophenoxytriazine host-guest compounds are reported and discussed. They feature inclusion of C60 into cages of 2,4,6-tris(4-iodophenoxy)-1,3,5-triazine [IPOT, hexagonal, P63/m, a=16.367(2)Å, c=20.661(4)Å, V=4793.1(13)Å3, Z=2] and of pyridine6-clusters into cages of 2,4,6-tris(4-bromophenoxy)-1,3,5-triazine (BrPOT, rhombohedral, R $$\bar{3}$$ , a=15.5186(8)Å, c=39.521(3)Å, V=8242.7(8)Å3, Z=6). The stackings of the threefold symmetric layers of XPOT host molecules are different from each other and from those of all previously reported XPOT inclusion compounds (X: Cl, Br, I). Graphical Abstract: The new compounds IPOT3·C60 and BrPOT2·py3, represent new packing types in the family of threefold symmetric XPOT inclusion compounds (XPOT=2,4,6-tris(4-halophenoxy)-1,3,5-triazine; X=Cl, Br, I

Tuning the activity of a hybrid polymer–oxocluster catalyst: A composition—selectivity correlation

Zr-based oxoclusters M$_{x}$O$_{y}$(OR)$_{w}$(OOR’)$_{z}$ are promising catalysts for the activation of hydrogen peroxide. However, they need to be integrated into suitable matrices to increase their hydrolytic stability and allow for their recovery after use. Polymeric materials can be successfully employed for this aim, since they modify the properties of the resulting hybrid materials, in terms of polarity and chemical affinity for the substrates, improving the catalytic activity. Herein, we report the synthesis of different acrylic polymers based on various co-monomers (methyl methacrylate (MMA), 2,2,2-trifluoroethylmethacrylate (TFMA) and 3-methacryloxypropyltrimethoxylsilane (MAPTMS)) covalently cross-linked by a Zr$_{4}$-based oxocluster, whose composition was tuned to optimise the catalytic oxidation of methyl p-tolyl sulphide. To assess their properties and stability, the materials were characterised via Fourier Transform Infrared (FT-IR) and Raman spectroscopies, Thermogravimetric Analysis (TGA), Solid-State NMR (SS-NMR) and X-Ray Absorption Spectroscopies XAS, before and after catalytic turnover

1-Bromo-2,3,5,6-tetra­fluoro-4-nitro­benzene

In the title compound, C6BrF4NO2, the nitro group is twisted by 41.7 (3)° with reference to the arene ring mean plane. The main inter­actions stabilizing the crystal structure include O⋯Br contacts [3.150 (2) and 3.201 (2) Å], while F⋯F inter­actions are minor [2.863 (3)–2.908 (3) Å]

Classification of wines by means of multivariate data analysis using the SPME/CGC-chromatograms of volatile aroma compounds

The solid phase microextraction (SPME) is an effective solvent-free sample preparation technique for the capillary gas chromatographic (CGC) analysis of volatile aroma compounds of wines. Using discriminant analysis based upon only two terpene compounds, it was possible to analytically discern between the varieties Riesling, Muller-Thurgau and Silvaner grown in the same region. The discrimination of these varieties was unsuccessful for wines of different vintages (1988-1995). In order to obtain a highly significant classification, it was necessary to consider further aroma components described in wine literature. The differentiation between these wines by a similar high classification rate was obtained using a set of variables selected by mathematical methods. Wines prepared from known grape varieties were qualitatively recognized by factor- and cluster-analyses as well as the relative peak intensities of the terpene compounds in the SPME-CGC chromatograms. The composition of wine blends was quantitatively determined

Spinning of Endless Bioactive Silicate Glass Fibres for Fibre Reinforcement Applications

Bioactive glasses have been used for many years in the human body as bone substitute. Since bioactive glasses are not readily available in the form of endless thin fibres with diameters below 20 µm, their use is limited to mainly non-load-bearing applications in the form of particles or granules. In this study, the spinnability of four bioactive silicate glasses was evaluated in terms of crystallisation behaviour, characteristic processing temperatures and viscosity determined by thermal analysis. The glass melts were drawn into fibres and their mechanical strength was measured by single fibre tensile tests before and after the surface treatment with different silanes. The degradation of the bioactive glasses was observed in simulated body fluid and pure water by recording the changes of the pH value and the ion concentration by inductively coupled plasma optical emission spectrometry; further, the glass degradation process was monitored by scanning electron microscopy. Additionally, first in vitro experiments using murine pre-osteoblast cell line MC3T3E1 were carried out in order to evaluate the interaction with the glass fibre surface. The results achieved in this work show up the potential of the manufacturing of endless bioactive glass fibres with appropriate mechanical strength to be applied as reinforcing fibres in new innovative medical implants

Highly fluorinated naphthalenes and bifurcated C–H⋯F–C hydrogen bonding

The synthesis and crystal structures of 1,2,4,5,6,8-hexafluoronaphthalene and 1,2,4,6,8-pentafluoronaphthalene are reported. Intermolecular interactions are dominated by offset stacking and by C–H⋯F–C hydrogen bonds. For hexafluoronaphthalene, molecules are linked in layers with (4,4) network topology via R12(6) C–H⋯(F–C)2 supramolecular synthons that are rationalised by consideration of the calculated electrostatic potential of the molecule. Such an arrangement is prevented by the additional hydrogen atom in pentafluoronaphthalene and molecules instead form tapes via an R12(8) (C–H⋯F)2 synthon. The geometric characteristics of C–H⋯(F–C)2 bifurcated hydrogen bonds have been analysed for crystal structures in the Cambridge Structural Database (6416 crystal structures; 9534 C–H⋯(F–C)2 bifurcated hydrogen bonds). A geometric analysis of these hydrogen bonds has enabled the extent of asymmetry of these hydrogen bonds to be assessed and indicates a preference for symmetrically bifurcated interactions

Spinning of Endless Bioactive Silicate Glass Fibres for Fibre Reinforcement Applications

Bioactive glasses have been used for many years in the human body as bone substitute. Since bioactive glasses are not readily available in the form of endless thin fibres with diameters below 20 mu m, their use is limited to mainly non-load-bearing applications in the form of particles or granules. In this study, the spinnability of four bioactive silicate glasses was evaluated in terms of crystallisation behaviour, characteristic processing temperatures and viscosity determined by thermal analysis. The glass melts were drawn into fibres and their mechanical strength was measured by single fibre tensile tests before and after the surface treatment with different silanes. The degradation of the bioactive glasses was observed in simulated body fluid and pure water by recording the changes of the pH value and the ion concentration by inductively coupled plasma optical emission spectrometry; further, the glass degradation process was monitored by scanning electron microscopy. Additionally, first in vitro experiments using murine pre-osteoblast cell line MC3T3E1 were carried out in order to evaluate the interaction with the glass fibre surface. The results achieved in this work show up the potential of the manufacturing of endless bioactive glass fibres with appropriate mechanical strength to be applied as reinforcing fibres in new innovative medical implants

Aromatic N versus aromatic F: bioisosterism discovered in RNA base pairing interactions leads to a novel class of universal base analogs

The thermodynamics of base pairing is of fundamental importance. Fluorinated base analogs are valuable tools for investigating pairing interactions. To understand the influence of direct base–base interactions in relation to the role of water, pairing free energies between natural nucleobases and fluorinated analogs are estimated by potential of mean force calculations. Compared to pairing of AU and GC, pairing involving fluorinated analogs is unfavorable by 0.5–1.0 kcal mol−1. Decomposing the pairing free energies into enthalpic and entropic contributions reveals fundamental differences for Watson–Crick pairs compared to pairs involving fluorinated analogs. These differences originate from direct base–base interactions and contributions of water. Pairing free energies of fluorinated base analogs with natural bases are less unfavorable by 0.5–1.0 kcal mol−1 compared to non-fluorinated analogs. This is attributed to stabilizing C–F…H–N dipolar interactions and stronger N…H–C hydrogen bonds, demonstrating direct and indirect influences of fluorine. 7-methyl-7H-purine and its 9-deaza analog (Z) have been suggested as members of a new class of non-fluorinated base analogs. Z is found to be the least destabilizing universal base in the context of RNA known to date. This is the first experimental evidence for nitrogen-containing heterocylces as bioisosteres of aromatic rings bearing fluorine atoms